1. Field of the Invention
The invention is an improvement to two-phase helical mixed flow impellers used in compression or expansion devices.
The invention notably applies to compression helical axial flow impellers such as those described in the Assignee""s French Patent Applications 2,333,139, 2,471,501 and 2,665,224, wherein the fluid occurs in the form of a flow in a substantially cylindrical shell.
The invention can also apply to expansion impellers where energy transfer occurs from the fluid to the rotor.
2. Description of the Prior Art
The prior art notably describes helical axial flow type impellers comprising a cylindrical open outer shell and a circular inner shell in the meridian plane, closed by a boss.
The invention relates to an improved impeller which imparts energy to or receives energy from a multiphase fluid comprising at least one gas phase and at least one liquid phase, the impeller comprising an inlet section and an outlet section, at least one flow channel defined by at least one boss and two successive vanes. The impeller of the invention has an axial length Lt and a mean radius of curvature Rh(z) (taken in the meridian plane), radius of curvature Rh(z) being determined over at least part of length Lt to limit separation of the phases of the multiphase fluid inside the channel.
The terms multiphase (or two-phase) compression or multiphase (or two-phase) pumping are used indiscriminately hereafter.
In the description hereafter
xe2x80x9cmeridian plane of an impellerxe2x80x9d designates any plane passing through the axis of rotation,
xe2x80x9cradial plane of an impellerxe2x80x9d designates any plane perpendicular to the axis of rotation,
xe2x80x9cchannel of the impellerxe2x80x9d, is defined by at least two successive vanes, an inner wall and an outer shell.
The expression xe2x80x9cmultiphase fluidxe2x80x9d designates hereafter:
either a -single-phase gaseous or exclusively liquid fluid in which a gas is totally dissolved,
or a multiphase fluid comprising notably a liquid phase and a gas phase, possibly solid particles such as sand, or viscous particles such as hydrate agglomerates. The liquid phase can consist of several liquid of different natures, and the gas phase can similarly consist of several gases of different natures.
The mean radius of curvature Rh(z) is for example determined from a known initial radius of curvature by implementing at least the following stages:
a value Z0 is selected on the axial position, the corresponding value of Anc(z) is known,
a starting value At_max=At_max_I valid for all the values of z is selected,
Ac(z) is calculated:
the known value of Anc(z) is compared with the value of At_max,
a) Anc(z) less than =At_max, then Ac(z) can have any value ranging between 0 and At_maxxe2x88x92Anc(z) with       Rh    ⁡          (      z      )        =      -                                        (                          W              ⁢                              xe2x80x83                            ⁢              sin              ⁢                              xe2x80x83                            ⁢              β                        )                    2                ⁢        cos        ⁢                  xe2x80x83                ⁢        γ                    Ac        ⁡                  (          z          )                    
and one of these values is selected,
b) Anc(z) greater than At_max, then Ac(z)=At_maxxe2x88x92Anc(z), with       Rh    ⁡          (      z      )        =      -                                        (                          W              ⁢                              xe2x80x83                            ⁢              sin              ⁢                              xe2x80x83                            ⁢              β                        )                    2                ⁢        cos        ⁢                  xe2x80x83                ⁢        γ                    Ac        ⁡                  (          z          )                    
c) the curvature and the slope are determined from the impeller inlet to the impeller outlet by starting from point T(ZO), T, is obtained at the inlet, corresponding to an angle xcex31, and T2 is obtained at the impeller outlet, corresponding to an angle xcex32,
It is determined if the angle y, corresponding to slope T(z), ranges between xe2x88x9290 and +90 degrees; if the angle becomes less than xe2x88x9290 degrees or greater than 90 degrees at any point, u value At_max_1 is decreased and calculation of Ac(z) is reiterated until an angle value belonging to a given [xcex31; xcex32] range is obtained.
The value corresponding to the minimum Anc(Z0) value can be selected as the initial value of Z0.
The values of angles xcex31 or xcex32 are for example selected to be equal or different.
According to one embodiment, the impeller is provided with an additional element placed on the outer shell of the vanes to limit leakage between the inlet and the outlet of the impeller, the element being situated for example at least at the high-pressure end of the impeller.
The invention also relates to a method for manufacturing an impeller as described above. The method comprises at least the following steps:
The initial radius of curvature of the impeller being known,
a value Z0 is selected on the axial position, the corresponding value of Anc(z) being known,
a starting value At_max=At_max_1 valid for all the values of z is selected,
Ac(z) is calculated:
the known value of Anc(z) is compared with the value of At_max,
a) Anc(z) less than =At_max, then Ac(z) can have any value ranging between 0 and At_maxxe2x88x92Anc(z), with       Rh    ⁡          (      z      )        =      -                                        (                          W              ⁢                              xe2x80x83                            ⁢              sin              ⁢                              xe2x80x83                            ⁢              β                        )                    2                ⁢        cos        ⁢                  xe2x80x83                ⁢        γ                    Ac        ⁡                  (          z          )                    
and one of these values is selected,
b) Anc(z) greater than At_max, then Ac(z)=At_maxxe2x88x92Anc(z) with       Rh    ⁡          (      z      )        =      -                                        (                          W              ⁢                              xe2x80x83                            ⁢              sin              ⁢                              xe2x80x83                            ⁢              β                        )                    2                ⁢        cos        ⁢                  xe2x80x83                ⁢        γ                    Ac        ⁡                  (          z          )                    
c) the curvature and the slope are determined from the impeller inlet to the impeller outlet by string from point T(Z0), T1 is obtained at the inlet, corresponding to an angle xcex31, and T2 is obtained at the impeller outlet, corresponding to an angle xcex32,
It is determined if the angle xcex3corresponding to slope T(z) ranges between xe2x88x9290 and +90 degrees; if the angle becomes less than xe2x88x9290 degrees or greater than 90 degrees at any point, value At_max_1 is decreased and calculation of Ac(z) is reiterated until an angle value belonging to a given [xcex31; xcex32] range is obtained.
The invention also relates to a device which imparts energy to receives energy from a multiphase fluid comprising at least one gas phase and at least one liquid phase, the device comprising at least one housing and at least one impeller as described above.
According to another embodiment, the device comprises at least one impeller provided with an additional element placed on the outer shell of the vanes to limit leakage between the impeller inlet and outlet.
The impeller or the device according to the invention are particularly well-suited for petroleum effluent pumping.